The present invention relates to a reinforced cation permeable polymeric membrane, which for support and strength contains a reinforcement fabric embedded therein, and to a process of formation.
Polymeric cation permeable films, also called membranes, are known and have utility in membrane ion exchanger, reverse osmosis devices and electrolytic cells such as chlor-alkali cells for the manufacture of chlorine, caustic soda and hydrogen. For commercial use, these films are generally reinforced with a fabric to impart strength.
U.S. Pat. Nos. 3,770,567; 3,849,243; 3,902,947 and 3,925,135 are directed to reinforced cation permeable membranes and methods of manufacture in which a support material is embedded in the membrane.
In these patents various embodiments initially employing a film containing a first polymer layer with sulfonyl groups present as cation exchange groups and a second polymer layer with sulfonyl groups present as --SO.sub.2 M wherein M represents a halogen atom are disclosed. These latter sulfonyl groups do not function for ion exchange. Thereafter a support material, e.g., a reinforcement fabric, is laminated under vacuum conditions to the polymer layer containing sulfonyl groups present as --SO.sub.2 M whereby the support material is embedded in this polymer layer.
After embedment of the support material, cation permeability is introduced across the thickness of the film by conversion of sulfonyl groups present as --SO.sub.2 M into cation exchange groups. Examples of cation exchange groups include --(SO.sub.2 NH.sub.2).sub.m Q or --(SO.sub.3).sub.n Me wherein Q is H, cation of an alkali metal or cation of an alkaline earth metal and m is the valence of Q and Me is a metallic cation and n is the valence of Me.
In U.S. Pat. Nos. 3,770,567; 3,849,243; 3,902,947 and 3,925,135, the thickness of reinforcement fabric controls the minimum thickness of the membrane since the fabric is laminated to and embedded in a layer of polymer. Some fibers of the reinforcement fabric are near to the surface of the membrane.